Modern manufacturing processes and equipment

Cutting processes

Cutting involves three basic operations: making the marker, spreading the fabric, and chopping the spread fabric into the marked sections. The marker, or cutting lay, is the arrangement of patterns on the spread fabrics. When hides are cut, the lay length is the hide size; many hides are cut in single plies. Short lengths are spread by hand, but large lays, made from large bolts of material, range in length to over 100 feet (30 metres) and heights containing hundreds of plies and must be spread with traveling spreading machines. Stationary spreaders are used for small sample lots. Manual and semiautomatic spreading machines are propelled manually over the lay length as the machine feeds the fabric ply onto the cutting table. Some machines book-fold the successive plies as the fabric is spread; others have turntable devices permitting one-way spreads. Lays may be spread either with all plies of fabric facing one way or with successive plies facing each other in face-to-face spreads. Turntable spreaders were introduced in 1920, face-to-face spreaders in 1938, and electric-powered spreading machines that spread a full bolt automatically without manual attention in 1946. In 1950, cutting blades were invented to cut the ply at each end of the lay as it is spread. These cut-off spreaders are automatic. Electric-eye edge controls for precise superposing of plies became available on automatic machines in 1962. In 1969 piggyback automatic spreaders were introduced, which carry a second bolt that is spread as soon as the first bolt is on the lay.

The marker is superposed on the completed lay. Markers are made of one of three materials: the fabric being cut, an inexpensive felt of muslin-type cloth, or one of a variety of papers. When paper with a low coefficient of friction is used, the marker is fastened to the lay by stapling or two-sided adhesive stripping. Papers with an adhesive on one side can be heat-sealed to a fabric and are commonly used with woollens or soft fabrics. Photomarking machines are used for duplicating often-used paper markers. Many markers are first made in miniature, with precise scaled-down patterns to determine the optimum layout for minimal yardage; the optimal miniature marker is then used as the guide for making the full-scale cutting marker. Some automated equipment is capable of both making the graded pattern and laying it out on the fabric to minimize waste. A sprayer machine, which sprays the entire length of the lay around the pattern, eliminates the need for manual marking-in.

Six types of machines are available to chop or cut a lay into the component parts of the marker: rotary blade machines; vertical reciprocal-blade machines; band knives, similar to band saws; die clickers, or beam presses; automatic computerized cutting systems with straight blades; and automated computerized laser-beam cutting machines.

Round-knife machines rotate a circular blade down into the lay, whereas straight-knife machines oscillate a straight blade in and out of the lay in jigsaw fashion. Both machines are portable manual-paced machines; that is, the machine is pushed through the lay as the blade cuts. Some models have dual speed controls and automatic blade sharpeners. In band-knife cutting, blocks cut from the lay with round or straight-knife machines are trimmed precisely to pattern specifications as the blocks are manipulated against the band-knife rotating in a fixed orbit. Though most band-knife machines are stationary, some are mounted on traveling platforms that carry machine and operator along the entire length of the cutting table, permitting band-knife cutting at any point of the lay.

Round-knife machines vary in diameter and rotary speed of the blade. Vertical and band blades come in circular, waved, or sawtooth perimeters. Vertical blade edges may be straight, waved, notched, serrated, or striated; band blades may be straight, waved, or saw-toothed. Straight-edge blades including the circular perimeter of rotary blades are used generally; the others are special-purpose blades.

Die clickers cut by pressing dies, superposed on the lay, through the depth of the lay. The cutting dies outline the patterns to be cut. Die presses are stationary or traveling; traveling die presses cover the entire width of the lay and move throughout the lay length and press dies into the fabric with intermittent strokes across the lay width until the entire lay is cut. In stationary clickers, the lay or section of the lay is pulled under the pressure beam for each die cutting stroke. Machine cutting of footwear, bags, pocketbooks, and similar items is done with die presses.

In automatic computerized cutting systems, introduced in 1967, the lay is covered with a thin plastic film drawn firmly to the lay by a vacuum operating through a porous cutting table and the porous fabric of the lay. The vacuum pulls the impermeable film firmly onto the lay, preventing any movement during the cutting action. There are two types of cutting actions: the lay may be stationary and the knife move, or the lay may move forward and the knife move horizontally.

A cutting system introduced in 1971 employed a computer-controlled laser beam to burn, or vaporize, the fabric rather than cut it. Unlike other methods requiring the accumulation of large orders before it becomes efficient to cut a specific style, the laser system, which provided for storage of programmed cutting instructions, allowed one complete garment to be cut at a time from a single layer of material. Among the advantages claimed for the system are the elimination of variations within a specific size, improved cloth utilization, efficient production of smaller orders, lower inventory requirements, and faster delivery.

Two types of auxiliary cutting equipment are used: cutting drills to drill holes through the superposed plies in a lay, and notches to notch the perimeters of the cut sections. These holes and notches guide the sewing operations. Cut sections are ticketed to ensure proper sizing and shading during the assembly of the garment.

Sewing production

Clothing, footwear, and allied industries have been known as the needle trades because sewing is the major assembly and decorative process used. Some items such as plastic raincoats and footwear are assembled and decorated by fusing, but only a tiny fraction of garments were produced completely by fusing, cementing, or mold casting.

Over 10,000 different models of industrial sewing machines have been made. Most are produced in Great Britain, Germany, Italy, Japan, and the United States. Sewing machines are classified according to stitch type and bed type (the shape of the machine’s frame). The seven basic beds, or frames, are flatbed, raised-bed, post, cylinder, off-the-arm, closed-vertical, and open-vertical. The bed type is determined by the manner in which fabric passes through the machine as it sews. There are four categories with regard to operational control, all electrically powered: manual-paced, automatic cycle with manual loading and extraction, fully automatic, and automated.

The prime characteristic of a sewing machine is the stitch it makes. Until 1926 stitches were classified inconsistently, with trade terms that often varied from one place to another and even from shop to shop. In 1926 the U.S. government became the first government to issue a seam and stitch classification to specify its requirements. During the 1960s other countries began to adopt the latest versions of these specifications for sewing equipment and sewn products, and these specifications were adopted throughout the world for industrial sewing.

The first hand-powered sewing machines in the 19th century sewed 20 stitches per minute. At the turn of the century some electrically powered machines sewed 200 stitches, and by the mid-20th century machine speeds had reached 4,500. By 1970 most machines could sew 7,000, and some could sew 8,000 stitches per minute. The first integrated sewing machine was introduced in 1969 by the Singer Company. Before that, manual-paced sewing machines had a separate clutch motor with start, speed, and braking controlled by foot treadle action; a belt drive ran the machine via treadle action to the motor’s clutch, which actuated or stopped the belt drive while the motor ran continuously. The integrated sewing machine eliminated the separate motor, its clutch, and the belt drive. The integrated machine frame contains the motor module, which is actuated, controlled, and stopped by a four-speed switch operated by a device resembling the former foot treadle. The motor in this machine rotates only when the treadle is actuated, so electricity is used only when the machine is sewing.

Special-purpose machines sew automatic cycles for operations such as buttonholing, button sewing, contour seaming, profile stitching, seaming for patch pockets, dart stitching, tacking, welt pocketing, and padding cycles such as blindstitching interlinings to the outer shell. Semiautomatic special-purpose machines are manually reloaded after each task; in automatic machines reloading and extraction are both done by the machine. Contour seamers are sewing machines that sew curved seams automatically; most such machines were semiautomatic by 1970. Profile seamers and stitchers seam or stitch angular or curved designs in which a backtrack path, such as a U seam or an angled seam (a square U), is sewed. These machines too were semiautomatic by 1970.

A sequential sewing machine introduced in the 1960s repeatedly sews an automatic cycle on the same garment with predetermined spacing between the operations. A sequential buttonhole machine, for example, sews five buttonholes on a shirt front automatically, one after the other, with given spacing. Sequential sewing machine modules are synchronized automatic systems of two or more sewing machines that sew the operation in series; the first machine completes its operation, the garment or section is fed into the second machine for the next operation, etc. For example, the first machine sews the centre front placket of a shirt front; the second machine sews a series of buttonholes on the placket. In tandem-machine arrangements, two machines sew simultaneously on the same unit. Gang-machine operation is an arrangement of three or more machines operating automatically under the care of one operator. The introduction in 1930 of stop-motion devices for stopping a sewing machine when the thread broke or ran out made gang-machine operation possible, as well as tandem machines in the 1940s and sequential machines and modules in the 1960s.

Before 1950 most industrial sewing machines had only the basic mechanical-linkage system of shafts, cams, gears, rods, belts, chains, and pulleys, with manual lubricating systems. Higher speeds, fully automatic cycling, and automatic sequential systems were developed later and were made possible by automatic lubrication systems with pumps and reservoirs, fluidic controls, and electronic controls.

The quality of manual-paced sewing depends on the integration of six variables: the needle and its size, shape, and finish; the type of feed system; the coordination of needle and feed; thread tension adjustments; the thread; and operator handling. Seam slippage, yard severance, puckering, elongation, gathering, and feed mark off are some of the quality areas affected. Machine manufacturers make needles in a variety of diameters, point shapes, and finishes as well as different types, shapes, and sizes of feeds and presser feet to improve quality and output.

Sewing machine attachments are jigs and fixtures used with sewing machines to decrease downtime (the time a machine is inoperative) and thus increase productivity by getting the fabric to the needle, aligning and repositioning fabric under the needle, or extracting and disposing of the sewed materials sooner. Trade terms for some of these sewing aids are needle positioners, stackers, programmers, guides, hemmers, binders, thread trimmers, stitching templets, seam folders, pipers, and shirrers. Needle positioners automatically set the needle in or out of the sewn materials as desired when the machine stops. Stackers extract and dispose the sewed sections with one of five actions: flipping, sliding, lifting, shuttle-drop, or conveyor cycle. Programmed sewing is an automatic sewing cycle induced by a module set to control the time sequence of initial positioning, sewing, repositioning if needed, thread trimming, extraction, and disposal. The times and sequence of these elements in the sewing operation may be changed for different sewing cycles. Automated sewing is a self-correcting system when the section sewed varies beyond given tolerance limits.

Fusing and cementing are two major processes for stitchless or decorative seaming in apparel and allied production. In fusing, the seam bond or decoration is formed by melting some fibre or finish content in the material in a manner that joins the sections or decorates in the desired area. In cementing, the bond, or decoration, is made by an adhesive, such as cement, glue, or plastic, which is applied to the materials during or immediately preceding the cementing process. Fusing is either by direct heat; by hot-head fusing presses, in which pressure surfaces are heated by electric heating grids or steam; or by electronic high-frequency or infrared systems. Cementing processes use mechanical-pressure systems with or without heat application, depending on the adhesive and materials used. Fusing, introduced in the 1950s, replaced sewing in some operations such as joining interlining to collars, cuffs, and coat fronts as well as seaming clothing and footwear made from certain synthetic yarns or plastic films.

Pressing and molding processes

Molding is any process that changes the surface characteristics or topography of a garment or shoe or one of its sections by application of heat, moisture, or pressure. Pressing, pleating, blocking, mangling, steaming, creasing, curing, and casting are trade terms for various molding processes in producing clothing and footwear.

Pressing has two major divisions: buck pressing and iron pressing. A buck press is a machine for pressing a garment or section between two contoured and heated pressure surfaces that may have steam and vacuum systems in either or both surfaces. Before 1905 all garment pressing was done by hand irons heated directly by gas flame, stove plate heat, or electricity; the introduction of the steam buck press changed most press operations. The first pressing machines had no pressure, heat, or steam controls such as those built after 1940. Modern buck presses are made to fit certain garment sections, such as a jacket front, pant leg, pant top, or shoulder area for a specific style and size. These improved buck presses have gauges to measure and control steam pressure and temperature, mechanical pressure, vacuum, and the press cycle time. Cycle-time controls permit one operator to work a series of machines. For example, a presser handles four presses doing the same or different operations; by the time a worker has finished extracting and loading the fourth machine, the first machine is ready for extraction and reloading. Cycle-time controls apply and shut off steam and vacuum action and open the pressing machine automatically. Conveyor buck presses, which may move intermittently or continuously, are buck-pressing systems in which sections or garments to be pressed are fed into a buck press and extracted from it by a conveyor belt.

In iron pressing, a hand iron functions as the top pressure surface. The two major types of hand irons are steam ejectors and dry irons. Electric hand irons are equipped with thermostats that regulate temperature. Steam-heated irons, whether ejection or dry, have fixed temperatures depending on the pressure of the steam supplied to the iron. Many hand irons are equipped with lift devices and gear drives to control stroke rate and minimize operator fatigue. Hand irons are made in a variety of sizes, weights, shapes, and surfaces; the specific usage determines the combination.

Special footwear processes

Footwear may be classified according to the section of the foot it covers and how it is held on: sandals, slip-ons, oxfords, ankle-support shoes, and boots. The term shoe refers to footwear exclusive of sandals and boots. Sandals cover only the sole and are held onto the foot by strapping. Slip-ons cover the sole, instep, and may or may not cover the entire heel; styles include pumps and moccasins. Oxfords cover the sole, instep, and heel and have closures such as laces, straps, buckles, buttons, or elastic to secure the shoe to the foot. Ankle-support shoes cover sole, instep, heel, and ankle and secure the shoe to the foot with a closure device; the chukka is an ankle-support style. Boots cover the foot from the sole to various heights above the ankle: shin height, calf length, knee length, and hip length. Closures may or may not be used, depending on the degree of snugness desired.

Most footwear factories that produce dress, play, and work footwear in slip-on, oxford, ankle-support, and boot categories from leather or synthetics simulating leather have eight processing departments: (1) cutting; (2) stitching, which sews the upper section above the sole; (3) stock fitting, which prepares the sole section; (4) lasting, which attaches the upper and its lining to a wooden foot shape, the last, in order to assemble the sole section to the upper; (5) bottoming, which attaches the sole to the upper; (6) heeling, which attaches and shapes the heel bottom into its final form; (7) finishing, which includes polishing, extracting the lasts, stamping the shoe brand and name on the sole, inserting heel and sole pads, and inspecting the inner shoe; and (8) treeing, which includes attaching laces, bows, and buckles and final cleaning and inspection.

There are three basic methods of attaching soles to uppers. The bottoming may be done by sewing, cementing, nailing, or a combination of these three joining techniques. Nailing includes the use of nails, screws, staples, or pegs. Sewing may be performed with or without the use of welt, insole, middle sole, and filler sections; the same applies to cementing soles to uppers. Sole sections vary in ply count; a three-ply sole has a middle sole sandwiched between outer sole and inner sole; the two-ply sole consists of outer and inner sole; the single sole has only one ply.